Hundreds of medicines have been rationed because pharmacies are selling drugs abroad to profit from the weakness of the pound.

Sterling's slide against currencies such as the euro, means that the UK has become a cheap place for foreign pharmacies to source drugs.

Some British pharmacies are cashing in by over-ordering drugs, a practice known as skimming', and selling to this overseas market.

Shortage: There are fears some patients could die because of difficulty in getting hold of drugs (picture posed by models)

But the exports have led to temporary shortages here. And there are fears that some patients could die because they cannot get hold of the drugs they need.

As a result, drug wholesalers have restricted the supply of 370 medicines in danger of running out, to pharmacies believed to be skimming. Orders for the medicines most at risk of running low are being monitored by manufacturers and wholesalers.

However, the combination of rationing and skimming means that it is harder for many pharmacists to obtain some drugs.

Increasingly they have insufficient stocks to meet demand and patients are being made to wait.

Stomach ulcer treatment Nexium and Plavix, for heart attacks and strokes are two of the 25 drugs that pharmacists are struggling to get hold of, said the Pharmaceutical Services Negotiating Committee.

AstraZeneca said there had been 'isolated incidents of shortages [of Nexium], which have been dealt with easily'. But he added: 'If we continue to see an increase in the number of pharmacies trading medicines outside the UK, it's not possible to rule out potential shortages.'

Pharmacists exported an estimated £30million of drugs intended for the UK in March, according to data consultancy IMS Health. A year ago there were virtually no such exports.

About 10 per cent of our pharmacies are involved in 'parallel exporting', it added.

Skimming, which is not illegal, has been further fuelled by a 5 per cent price cut on prescription medicines bought by the NHS.

David Baker, of the Dispensing Doctors' Association, said: 'This is a very, very serious problem and the result could be that somebody can't get the medicine that they need and dies.'